What’s the Trouble With Sweet Potatoes?

We’re continuing with a series on people who have reported something going wrong when they tested some variation of the Perfect Health Diet. (The first post summarized experiences, good and bad; the second looked at difficulties suddenly adding carbohydrates to a very low-carb diet.)

The next issue was reported by Chris Masterjohn; he had trouble with sweet potatoes:

Although sweet potatoes are considered a safe starch on the Perfect Health Diet, they are not very safe for me. When I discovered how yummy sweet potato fries are, I started eating several sweet potatoes per day. Within a few days, I was limping and my neck was stiff. By the end of the week, my limp was extreme. I looked online to see if I was eating anything high in oxalates, and sure enough, sweet potatoes are loaded with them. My symptoms dramatically improved after one day off sweet potatoes and were gone the second day.

I’ve been very achy since I started eating sweet potatoes daily. Why would some of us be maladapted to oxalates?… I’m wondering if after a long stint of LC/paleo eating I’ve become intolerant to oxalates or to starch in general.

Clearly sweet potatoes are not safe for everyone. What might be causing the trouble?

Fructose and Fiber as Possible Confounders

One factor to consider is that there are different varieties of sweet potato. We eat an Asian sweet potato variety which is not nearly as sweet as conventional American sweet potatoes; it has a yellow flesh and a chestnut flavor. It is botanically a yam, not a sweet potato. It looks like this (via “my super sweet twenty-six”):

Like so many modern foods, the standard American sweet potato has been bred for sweetness. Here is data from http://nutritiondata.com comparing 100 g of potatoes, yams, sweet potatoes, and grapes for sugar, starch, and fiber content:

Food

Sugar (g)

Starch (g)

Fiber (g)

Potato

1.2

17.3

2.2

Yam

0.5

23.1

3.9

Sweet potato

6.5

7.5

3.3

Grapes

15.5

0.0

0.9

All have similar calories. Yams are largely sugar-free, but sweet potatoes are intermediate between grapes and potatoes in both sugar and starch content. They are sort of half fruit, half starch.

Thus, it is conceivable that sweet potatoes could trigger an issue like fructose malabsorption; or that fructose or fiber might feed certain gut infections that would not be similarly fed by potatoes.

Oxalate

Chris believed his problem was due to oxalate. Sweet potatoes do contain oxalate, although they are not the only plant foods which do.

In fact, by far the largest source of oxalate in the American diet is spinach. Spinach by itself accounts for over 40% of all oxalate consumed by Americans; potatoes for about 10%. [1] Wheat bran has high levels of oxalate.

Why are oxalates troublesome? Some people have sensitivities to oxalate. Rarely, genetic defects in the enzymes that degrade oxalate cause a disease called primary hyperoxaluria; this disease afflicts 1 to 3 people in a million. Other conditions can elevate calcium or oxalate in the urine and increase the risk of calcium oxalate kidney stones. This is especially likely in people who are deficient in magnesium or who don’t eat citrate. [2]

Another pathway by which oxalate might cause trouble is via fungal infections. Candida and other fungi form calcium oxalate crystals in tissue [3,4]; fungi appear to be responsible for the yellow-brown calcium oxalate biofilms which form on stone monuments. [5]

But the literature suggests that oxalate sensitivities are rare. If oxalate sensitivity is present, then it should manifest itself when eating spinach, wheat bran, and other oxalate rich foods. Since Chris has praised spinach and wheat recently, I wonder if it is really the oxalate that caused his trouble.

Phytoalexins

Another possibility is a class of toxins called phytoalexins.

Ordinarily, sweet potatoes are largely toxin free. But when attacked by fungus or molds, sweet potatoes generate a variety of food toxins. As two papers describe them:

Sweet potatoes contain phytoalexins that can cause lung edema and are hepatotoxic to mice. At least one of these, 4-ipomeanol, can cause extensive lung clara cell necrosis and can increase the severity of pneumonia in mice. Some phytoalexins in sweet potatoes are hepatotoxic and nephrotoxic to mice. [6]

Ipomeanine (IPN), 4-ipomeanol (4-IPO), 1-ipomeanol (1-IPO), and 1,4-ipomeadiol (DIOL) are toxic 3-substituted furans found in mold-damaged sweet potatoes. IPN and 4-IPO are the most toxic, but all produce pulmonary toxicity in cattle and rodents, and 4-IPO induces hepatotoxicity in humans. [7]

Cattle will die if fed mold-damaged sweetpotatoes:

Unfortunate bovine fatalities occurring after ingestion of mold-damaged sweetpotatoes preclude the use of the culled tubers in livestock feed. In cattle, mold-damaged sweetpotatoes induce an acute respiratory distress syndrome resulting in asphyxiation. [8]

Toxins may be present even if mold damage is not visible:

Fermentation of 6 weeks duration was observed to inadequately eliminate the lung, liver, and kidney toxicity caused by mold-damaged sweetpotatoes. In fact, fermentation exacerbated the hepatotoxicity of mold-damaged sweetpotatoes. This is also the first demonstration that sweetpotato regions lacking visible mold damage can induce lung and kidney injury … [8]

Allergies

Sweet potatoes are generally considered to be one of the least allergenic of foods. However, infants sometimes do have sensitivities to sweet potato. This may reflect an immature gut flora in the infants; perhaps specific bacterial species — possibly including the oxalate-digesting Oxalobacter [9] — make sweet potatoes tolerable? If so, it raises the possibility that adults with incomplete gut flora might also have sweet potato sensitivities.

There is also the possibility of allergies to mold toxins in infected sweet potatoes.

Food Sensitivities as a Diagnostic Tool

Leaky gut. People with a leaky gut will have many food sensitivities; people with a healthy gut will have few.

Small bowel infections. People with infections of the small intestine will usually have a negative reaction to fructose.

Colonic infections. People with infections of the colon may react badly to fiber, and obtain relief on low-fiber diets.

There is a chance that oxalate may benefit fungal infections, so I suppose an oxalate sensitivity could be diagnostic for that, although in my experience fungal infections are usually slow-reacting to food and the response is rarely obvious.

Conclusion

In our book [p 121] we note that all plants make pesticidal toxins. Thus, no plant food can be guaranteed to be safe.

Normally, levels of pesticidal toxins are low in sweet potatoes. But it’s always desirable to inspect sweet potatoes for visible damage, and to discard any that are discolored or show other evidence of toxin production.

I confess to being puzzled as to how sweet potatoes caused Chris’s symptoms. If he tolerates spinach and wheat bran, it seems unlikely that the oxalate in sweet potatoes would be responsible. He might wish to test various foods and try to narrow down the source of his sensitivity.

For our part, we may cease listing sweet potatoes among our “safe starches” and specify yams instead, since a “safe starch” should probably be low in fructose.

166 Comments.

thks for your speedy reply.I got this to replace 25% of the flower used in baking, befor i got to the page in your book explaning the evils of flower, so have been adding it to soup’s.
the product i have has 15g of dietary fiber/serving size of 28g and 0 protein.
at the very least i would like to finish the 5lb container if there is a risk.
i won’t say the maufactures’s name hear not sure what your policy is, but if its of interest let me know.they say that the resistant starch helps feed the good bacteria in the colon.

I have just read your post on Dry eyes, constipation (i have both) and Glucose deficiency.

I have always eaten alot of carbs before starting this diet 1 month agao. My dry eye (poss Sjogrens symptoms) is why i am doing it, ive had it for years. So i was getting enough Glucose.

My question is- Does Sibo cause Glucose Malabsorbtion (as well as Fructose?)…Im wondering whether I am not absorbing Glucose- since I get gas when i eat fruit which is low Fructose- i.e pineapple. Indicating that fructose is not the only problem.

The response to fruits/pineapple indicates fructose malabsorption. This is fairly common and it does indicate some sort of gut dysbiosis and probably an excessive influx of endotoxins from the gut into the body (called endotoxemia).

If starch and fiber are fine, then the problem is in the small intestine, not the colon.

I would definitely add in white potatoes and white rice as long as they’re tolerated. Potatoes, especially refrigerated cooked potatoes (eg potato salad), have a lot of fiber.

There may also be some dysbiosis — limited/disturbed colonic bacterial population — causing the constipation.

I don’t know if it will cure the Sjogren’s but fixing the SIBO seems like the first course of action. Try to improve digestion first of all, probiotics and fermented foods may ease the constipation, better production of stomach acid (salt, betaine HCl), enzymes, intestinal tract mucus (DGL) may help.

Also, your doctor may be able to diagnose SIBO, H pylori, or some specific problem.

Im trying to work out why im intollerant to starch.. im fine with sugars, not good with fruits (so think maybe fructose problems) but anything with starch i have major problems.. does anyone have any clues?

That experience implies a gut dysbiosis — you have a bad mix of bacteria in your gut, usually an overgrowth of some species that shouldn’t be dominant, and when you eat starch you provide the bacteria with fiber that makes them more active and your immune system has to deal with what is essentially a post-meal infection in your digestive tract.

The fix is to re-shape your gut flora. Continue to eat small quantities of starch so that you feed beneficial bacteria which can digest those, try to increase the diversity of flora by eating fermented foods, try to improve immune function (esp vitamin D, vitamin A = liver optimization), and ideally get a stool test to look for treatable infections — Metametrix microbial ecology is good.

Hi Dr. Paul,
Please talk more about liver? I’ve read so much that iron is a major health concern (cancer, even with heme-bound),yet the Weston Price Foundation and yourself suggest liver is healthy. I’m confused, as it seems the mineral content is way out of balance to be healthy. Wouldn’t eggs and nutritional yeast provide a better approach for more balanced phospholipid mineral profile? Or is there something I’m missing? Thank you.

Iron is an important nutrient that we need but it does often become present in excess. However, that’s easily fixed by donating blood, which is a good thing to do. It’s not a bad idea to get tested periodically, but in general people who give blood regularly (or who menstruate) will not have an iron excess.

I have been intolerant to sweet potatoes for at least 16 years now. Even if I have a tiny bit (like mushed into couscous when I’ve removed all the whole pieces) I get severe stomach cramps, hugely bloated stomach and diarreah. I avoid anything pre made that has orange vegetables in it as the pain I get is so severe. I am also lactose intolerant and generally have a sensitive stomach. I avoid any root vegetables that are new to me (eg. Taro, yams) in case I have the same reaction. It’s very frustrating as so many healthy recipes seem to have sweet potato in them! I would love to know why I have a problem with sweet potato but for now I will continue to avoid them!

Hi, gemma, sounds like you have mannitol malabsorption. Look up the monash uni fobmap apphttp://med.monash.edu.au/news/2012/fodmap-app.html
They have the cutting edge research and a extremely helpful app. Which changed my tummy and quality of life 🙂
Celery and watermelon are also very high in mannitol.

I’m pretty sure what you have pictured here is a Japanese sweet potato, which really is the same species as our domestic orange sweet potato, whereas a true yam is an entirely different species. Please correct me if you think I’m wrong, but I did really a large amount of research on this while ago … Sweet potato is ipomoea batatas, which is in the morning glory family, and satsuma imo is ipomoea batata. See this page, for example: http://washokufood.blogspot.com/2008/07/satsuma-imo.html. True yams are dioscorea. According to Wikipedia, there are true yams in Japan, but they are the mountain yam (nagaimo or yamaimo) and Jinenjo (http://en.wikipedia.org/wiki/Dioscorea_opposita). I have wondered whether the USDA entry for “yams” is true yams or not, but I am not sure. It seems likely given how different the data are! However, even if they aren’t true yams, the Japanese sweet potatoes DO seem less troublesome to me also than the orange ones. In addition to fructose, there are sugar alcohols in sweet potatoes that trouble some people, because they are not digestible. If you look for materials about “FODMAPs” you can find some data on that I think. So I have wondered if there are possibly also fewer sugar alcohols in the yellow-fleshed variety? Not sure why, but I agree that for some reason the yellow ones seem easier to digest ….

Unlike Chirs, spinach and wheat bran and all nuts anything high oxalate causes me bad muscle pain and IC bladder disease pain. I am trying to follow this diet but with all high oxalate foods out it is very hard to adhere to. (high oxalate foods yaste good)I am going to start again soon!

Hi, I ate a lot of sweet potatoes for years (orange and white flesh), plus african and south american yams. many per day. Yam’s in particular are very vulnerable to mould/fungus and large parts of the crop are lost in transit.

I have IGE sensitivity to mould and have recently been diagnosed via DNA PCR Stool sample with mould/fungus GI infection (not candida strain). I do have other outstanding gut issues but recently i’ve begun almost allergy reacting to sweet potatoes/yams – would it be reasonable to assume that I could have picked up a fungal infection from a yam? I have eaten them in huge amounts over the years and always tried to avoid eating the mouldy parts but i wonder if i may have ingested mould by accident.

Paul, I’m confused about the debate regarding resistant starch. I started using RS since listening to Angelo Coppola’s podcast a week ago. I noticed an immediate improvement in digestion even though I have gut dysbiosis and RS is contra-indicated by many professionals. Last night I was gassy and felt some GERD. However, since my IBS-D which I have struggled with for 30 years is gone, I’m reluctant to stop. What do you think?

I found this thread googling “sore joints sweet potatoes” because I’m having that problem like Chris. I too discovered how delicious sweet potato fries were and started having a sweet potato several times a week. I’ve been paleo for three years now and on the autoimmune version with no eggs or nuts for several months. But joint soreness from RA has really continued unabated. If it’s not sweet potatoes, I give up, because I’ve eliminated everything else!

RA is due to infections, toxins, or autoimmunity triggered by bad gut microbes (essentially, a gut infection). Removing triggers may reduce symptoms but it can aggravate gut dysbiosis by creating malnourishment or a less diverse gut flora. So autoimmune versions of Paleo should be experimental in which you only restrict things you know are troublesome to you.

Thank you, Paul. That makes a lot of sense. I had great success with RA pain the first year I was on paleo, eliminating what were obviously triggers for me. But the past year or two despite, yes, eliminating still more things, I’ve had ongoing joint issues and pain. I’ve recently added back in white rice but tend to eat the same things over and over – fish, broccoli, cauliflower, broth, sweet potatoes, apples. I’ve even been avoiding spinach lately out of fear of oxalates. I really appreciate your suggestions and will start implementing them today!

Hi, I have a comment on the article above. The person Chris who the article is helping, mentioned that he started eating sweet potato french fries, which tells me that he is eating more than just sweet potatoes. He doesn’t state what kind of oil he is using, but he could very well be reacting to the oil, if it is an oil that shouldn’t be heated to a frying temperature, like canola or any seed oil or even olive oil. Heating these oils will cause them to become rancid and rancid oils cause inflammation, among many other issues. Just a thought that wasn’t mentioned. I eat sweet potatoes, but not sweet potato french fries. I looked up this article trying to find information on the glycemic index, which I’ve heard is lower than white potatoes, but in your chart, it says there is more sugar in a sweet potato. The information on the fungus is really interesting because I always notice that when I buy sweet potatoes in a bag, they often smell a little like mold, so I was them and boil them, but I wondered if this had anything to do with what you were referring to.

Based on recommendation in PHD, I tried Taro for the first time today, and what a great discovery this is!! This is like a softer version of potato, lighter flavor, and MUCH better glycemic index than American potato. Unfortunately, Taro does contain calcium oxalate so this is why I bring it up in context of the current thread.

My questions are:

1) Does the calcium oxalate concentrate in the skin, or is it dispersed evenly throughout the Taro? I am removing the skin before boiling in a pressure cooker.

2) I read online that the Taro contains both an insoluble and soluble calcium oxalate, and it is only the soluble calcium oxalate that can be removed by cooking. Does anyone have data on the relative quantities of each, and at what kind of dosage does one reach toxicity?

3) I read elsewhere that the calcium oxalate can be partially neutralized by putting a pinch of baking soda into the water before boiling. Does anyone understand the chemistry there?

4) Are there any guidelines for how long to soak or boil the Taro to minimize the calcium oxalate concentration? I boiled for ten minutes in a pressure cooker, and that absolutely demolishes the taro to a very soft and crumbly texture. But perhaps that method isn’t maximizing the removal of the calcium oxalate?

While I absolutely loved the Taro, I do unfortunately detect a slight burning sensation on my tongue and back of throat, so that is a classic sign that some of the calcium oxalate was there and I reacted to it. I eat a LOT of spinach everyday and do NOT react to calcium oxalate there, but perhaps the calcium oxalate in spinach is not leaching out while chewing, or just isn’t in a high enough dose?

Any references on this I would love to see. This is a fantastic food and it is worth learning how to prepare it for maximum safety.

I realize this was an old comment, but I’m answering one of the questions in hopes it may help someone anyway.

If you are trying to reduce oxalate content, boiling and throwing out the water is the preferred method. The soluble oxalate content of foods is leached into the cooking water, so you want to throw it out. For soaking foods 8-12 hours is a pretty common length, for longer soak times, changing the water 1-2 times is generally recommended.

If you want detailed information on oxalate and how it can affect health, the Trying Low Oxalates yahoo group is a fantastic resource, Susan Owens is the listowner.

I’m very late to this discussion, but sweet potato “fries” are often coated in flour 😈 to make them crispy. I’ve been glutened so many times because I’ve assumed they were gluten free and/or the waiter didn’t know. I no longer order them.

i have been eating carrots for a months now . i started eating 2 carrots a day . now i have my palms and soles have turned orange and my face is starting to turn orange too . 2 weeks back i started eating 1 sweet potato a day , i’m thinking to discontinue eating carrots cz of the discoloration . what about sweet potatoes ? is 1 potato per day gonna do the same carrots for me ? what i should do ? i’m 20 yrs old female .

Thank you very much for this useful information. I was wondering why I had a fructose reaction when I had sweet potatoe the other night. Now I know that it was the american type. I didn’t like it anyway, it was waaaay too sweet. Today I will give the white-fleshed kind of yam a try.

Hi! I bought Japanese sweet potatoes a few days before Christmas and a couple days ago, I baked one and put it in the fridge. It was kind of strangely colored inside and it was fairly dry so I decided to scoop some of it out to make gluten and dairy free sweet potato biscuits with. I made them and consumed several that night. I had been coming down with something and that night I was feeling really bad so when I woke up late night/early morning and was nauseous after taking a pill to try to make me feel better, I snacked on one and stayed up for a while later before falling asleep. I woke up with a really bad headache, pressures all over my face, nerve pain (which felt like shingles I’ve had previously), and achy pain in my neck. To tide me over, I started eating another biscuit, and when I bit into these dense goods, I noticed these small green 3dimensional “balls” or something in it. My mom broke open some of the remaining biscuits and noticed a couple similar green things in it (it wasn’t a surface thing). My mom thought it most have just been some greener flesh of the sweet potato that wasn’t mashed all the way but I thought otherwise since I new I had seen any in the dough or while eating it the night before so I didn’t eat any more. That evening (yesterday) I peaked in and notice this green thing covering a lot and even on the surface so I know it was a growth of some kind. I wish I took a picture but my mom threw them out right away. The largest ones were maybe about half a cm big. Does anyone know what this is? A mold, fungus, parasite, etc? It’s been two nights since I’ve eaten the first biscuits and I’m still achy and weak and my throat hurts a lot. I have no idea if this is a coincidence or if they’re related. Thanks for your feedback and help!

It sounds like mold. The main negative effect is usually from toxins, not a live infection. You can speed up detoxification and excretion of the toxins eating extra fiber, taking activated charcoal, and taking glutathione and bile supports (N-acetylcysteine, glycine, taurine, vitamin C).

I just thought I would add myself to the list of people who’ve experienced troubles from eating sweet potato (actually it troubled a few members of my family). Basically, if I ate a lot of it in one meal, I would get sores in my mouth, and a sore stomach. My sister also got a sore stomach. It took us a while to identify sweet potato as the potential culprit and, since eliminating it from my diet, I have never again experienced these symptoms. Btw, I’ve read the book and really enjoyed it.

Just a follow up. The symptoms I experienced were only associated with one dish we cooked at home: sweet potato, sometimes tomato, beef massaman (beef in a sauce, purchased from the local butcher), and coconut cream – all baked together in the oven. I have since eaten lots of baked and boiled sweet potato and have not experienced the same symptoms. I’ve never had an issue with tomato or beef, nor coconut cream (though I want to test this more). Therefore, it now seems the sauce that came with the beef was the most likely cause, unless it was a coincidence of the symptoms and meals. Oh, and while this dish seemed to exacerbated my sisters symptoms, they also seemed to be part of a broader issue.

I guess this stresses the importance of not jumping to conclusions and investigating every possibility.

Hi Paul,
I appreciate your research. I started home workout to gain wait and muscle. But I don’t want unnecessary fat get chance in this process. that’s why I started a new diet plan. In my new plan I included sweet potatoes in my breakfast with egg white and two bananas. in lunch whole wheat bread. in dinner white rice and curd. meanwhile I replaced my snacks with fruit salads. later I realised gas getting formed in my digestive system. I’m not sure where is the wrong. Please help me to fix my diet plan.

What in my opinion is probably not properly understood here, is that different food cause different effect on the various microbes that inhabit the body, mouth, intestine etc.

So it´s not only bacteria, but yeasts/fungi, parasites, viruses, kept in check with each other.

For example, let´s say someone that doesn´t eat any fruit, suddenly load up with oranges, experience after some days several ulcers in his mouth. These are caused by a virus (herpes) which now got the upper hand because it was no longer in balance with other microbes that was killed off via the vitamin C, citric acid, and enzymes in the raw orange.

The body can deal with such viruses over time, but what typically happens is that someone indulge in one type of food (say Kiwi fruit, or sweet potatoes), they normally never eat, and this cause a significant reaction and they conclude they cannot tolerate the food. I think it´s just the same for various digestive upsets, painful joints, eczema, food intolerances etc.

So one type of food (say fruits) may be good at killing off bacteria, but instead lead to yeasts or other micro-organisms (temporarily). Another type of food like vinegar (acetic acid) or coconut fat (shorter chain fatty acids), may not kill bacteria so effectively (they are produced by bacteria), but is more effective in dealing with viruses and yeasts.

A third type of food, the root vegetables, especially the raw carrot (which is somewhat like a mixture of potato and carrot), is designed to deal with the yeasts and bacteria in the wet soil, so it may help rid the body of those, causing a temporary flourishing of some other microorganism.

Certain mushrooms may have very strong properties against various microbes and be an extremely effective antibiotic for some.

Fungi are used to make many antibiotics. Penicillin is a compound derived from the penicillium fungi. Penicillium roquefortum is the major fungi used in roquefort cheese. Many people say they can´t tolerate such cheese.

Someone with the mentioned herpes virus that cause the mouth sores can just use some vinegar in a glass of water, several times per day, and it may quickly disappear.

The solution is simply to be cautious about new foods and introduce them in small quantities and gradually increase over time, giving the body time to adjust to the new situation.

A reason why egg whites cause reactions is that is a very powerful anti-microbial, designed to deal with many troublesome microbes. Raw egg white is more powerful than cooked.

It could be the beta carotene. I’m not sure about Chris’s medical history. However, I have a long history with vitamin A. I took a course of Accutane in 2000 and ever since then have had extreme trouble with both pre-formed vitamin A and beta carotene. I had mild toxicity symptoms at 5,000 IU per day from normal foods and did not realize that the symptoms were caused by the vitamin A until I eliminated it entirely from my diet. Then, I stupidly tried a dose of 100,000 IU of pre-formed A for a few weeks after reading studies indicating that it is safe even at these levels. I have mentioned this on other blog posts, but this led to severe gastrointestinal damage and brain problems. I had severe depression and memory loss for several weeks. I still have mild confusion from time to time. But, the brain symptoms are mostly gone. Still dealing with digestive issues. But, I think they will heal over time. I just tried to eat some sweet potato and had a negative reaction similar to the ones I had from the vitamin A. Confusion and digestive disturbances.

Some people, especially those who have negative reactions to Accutane, seem to be especially sensitive to vitamin A and/or beta carotene.

Me too! Oxalates! Thanks for writing & sharing this. I have tried sweet potatoes several different times now and they always give me severe back pain, neck and frankly every joint in my body aches. I haven’t eaten any white potatoes in a long time. It was home baked sweet potatoes with nothing added. In the past, if i continued to eat them for many days, I woudl develop vulvodynia pain down there, which starts with minor spasm/cramps. But, it goes away when i reduce my foods high in oxalate. I am also sensitive to Oxalates, i guess that’s the link.

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